1. Field of the Invention
The present invention relates to a composite solid tire and a method of producing the same, and particularly to advantageous techniques for renewing worn solid rubber tires.
2. Discussion of Related Art
As a tire that supports, in a vehicle such as an automotive vehicle or an industrial vehicle, a load and has the function of smoothly transmitting forces between the vehicle and road surface, there have conventionally been known two sorts of tires, i.e., a pneumatic tire having a hollow structure in which air is charged, and a solid tire having a solid structure constituted by a rubber-based annular body. In particular, the solid tire enjoys, as tire's functions, a load supporting property, a cushioning property, and a rubber elasticity, and is widely used in low-speed and high-load vehicles such as a forklift truck, an industrial tractor, a battery carrier, or a trailer. As predominant sorts of the solid tire, there are known a tire that is constituted by a single tread rubber and is directly bonded to a wheel, a tire that is constituted by a rubber adhered, by vulcanization, to a base band and is press-fitted onto a wheel, and a tire that is constituted by an annular tread rubber and is fitted on an outer circumferential portion of a wheel.
Generally, the solid tire is known as a solid rubber tire that is constituted by a tread rubber formed of, e.g., NR or SBR. Since the solid rubber tire contacts the road surface and produces a frictional force to allow movement of the vehicle, a surface of contact of the tire with the road surface is worn little by little as the tire is used for a long time and, if a life expectancy of the tire is fulfilled, the tire should be disposed of. Recently, however, the disposal of waste tires has become a serious social problem. In particular, since the solid rubber tires are heavier than pneumatic tires used in, e.g., passenger cars, the solid rubber tires are more difficult to handle. In addition, the solid rubber tires are hard to burn or find other applications. Thus, the solid rubber tires are very difficult to dispose of.
In the above-indicated technical background, Patent Document 1 (Japanese Patent Application Publication No. 5-31822) has proposed a pneumatic-type solid tire having a structure in which a surface of a tread portion of a worn tire is subjected to buffing as a sort of polishing and a renewing tread rubber is adhered to the thus polished tread portion. According to this technique, worn tires that have conventionally been difficult to dispose of can be effectively utilized, tire materials can be saved, and times needed to produce tires can be reduced.
However, even though the renewing tread rubber may be adhered to the tread portion of the worn tire, so as to produce a renewed tire, the tread portion of the renewed tire is easily worn again as it is used. Thus, the durability of the tread portion of the renewed tire is not satisfactorily improved. In addition, since rubber materials used to form the renewed tread rubber contain carbon black as a reinforcing agent and accordingly have a black color, black marks of the tire are left on the road surface because frictions are produced between the tread rubber and the road surface. The black tire marks left on the road surface may damage an aesthetic appearance of the road surface and, in a work field where a forklift truck or an industrial tractor is used, not only the black tire marks but also black rubber powder resulting from wearing of tires may damage a work environment.
In addition, Patent Document 2 (Japanese Patent Application Publication No. 2002-144442) discloses a wheel renewing method in which urethane rubber is used. More specifically described, this document discloses a renewed wheel obtaining technique in which, after a rubber portion is removed from a base band of a waste tire, an ether-based urethane rubber layer is formed on an outer circumferential surface of the base band.
In the above-indicated renewed wheel, the urethane rubber layer contacts road surface. The urethane rubber has a higher wear resistance than that of a common tread rubber formed of, e.g., NR or SBR. Thus, the renewed wheel can enjoy a significantly improved durability or life expectancy. On the other hand, the renewed wheel suffers a lower cushioning property than that of a wheel having the common tread rubber. Therefore, when an operator operates a vehicle, such as a forklift truck or an industrial tractor, in which the renewed wheel is used, uncomfortable shocks may be transmitted to the operator. The cushioning property of the renewed wheel might be improved by forming the urethane rubber layer to have a foamed structure or largely lowering the hardness (or increasing the softness) of the urethane rubber layer. In this case, however, the urethane elastomer may lose its proper wear resistance and accordingly its durability.